He actually doesn't, but a guy can take a few minutes to answer his own door, right? Especially when he's used to people either letting themselves in, or having someone else open things for him so he doesn't have to interrupt whatever it is that he's working on.

And he is working on something, so the second knocking is basically the first knock to him, and he's not sure what all the fuss is about when he opens the door.

'Like yelling at me when I have a hangover is going to make me want to come answer the door. What is it?'